The present invention relates to tertiary amines containing hydroxyl and surface active groups and the use thereof as catalysts for preparing polyurethane foams.
Polyurethane foams are widely known and used in the automotive, housing, and other industries. Such foams are produced by the reaction of a polyisocyanate with a polyol in the presence of various additives. One such additive is a chlorofluorocarbon (CFC) blowing agent which vaporizes as a result of the reaction exotherm causing the polymerizing mass to form a foam. The discovery that CFCs deplete ozone in the stratosphere has resulted in mandates diminishing CFC use. Production of water blown foams, in which blowing is performed with CO2 generated by the reaction of water with the polyisocyanate, has therefore become increasingly important. Tertiary amine catalysts are typically used to accelerate blowing, for example, the reaction of water with polyisocyanate to generate CO2, and gelling, for example, the reaction of a polyol with isocyanate.
The ability of the tertiary amine catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a particular polyurethane foam. If a catalyst promotes the blowing reaction to a too high degree, much of the CO2 will be evolved before sufficient reaction of isocyanate with polyol has occurred, and the CO2 will bubble out of the formulation, resulting in a collapse of the polymerization mass and yielding a foam of poor quality. In contrast, if a catalyst too strongly promotes the gelling reaction, a substantial portion of the CO2 will be evolved after a significant degree of polymerization has occurred. Again, poor quality foams which are characterized by high density, broken or poorly defined cells, or other undesirable features, will be produced.
Tertiary amine catalysts generally are malodorous and offensive and many have high volatility due to their low molecular weight. Release of tertiary amine during foam processing may present significant safety and toxicity problems, and release of residual amine from customer products is generally undesirable. On the other hand, low vapor pressure-high molecular weight amine catalysts are expected to require very high catalyst usage due to their low nitrogen/carbon ratio, making the manufacturing cost too high.
Amine catalysts which contain hydroxyl groups, as well as C6 or higher alkyl or fatty acid groups have shown good activity, making their usage level relatively modest despite their high molecular weight. Further, their high molecular weight, reduced volatility, and reduced odor can limit the exposure of operators and end users to offensive amine vapors. In addition, amine catalysts containing hydroxyl functionality can chemically bind into the urethane during the reaction, thus limiting their release from the finish product. Amine catalysts containing secondary hydroxyl functionality are generally preferred because they exhibit a desirable balance between their promotion of the active hydrogen-isocyanate reaction (gelling and blowing) and their own reactivity with isocyanates. It is therefore desirable to produce new tertiary amines and catalyst systems employing such tertiary amines that have increased catalytic activity, decreased usage levels, and increased ability to bind to the urethane matrix. It is also desirable to provide a method for producing polyurethane foams which employs such tertiary amine catalyst systems. It is to these ends that the present invention is directed.